Field of the Invention
The invention relates to an image heating device such as a fixing unit mounted in an image forming apparatus of an electrophotographic recording type, such as a copier or a printer, or a glossing device for improving a toner image in gloss by heating a fixed toner image on a recording material again. The invention also relates to a heater used for the image heating device.
Description of the Related Art
As an image heating device, there is a device having a cylindrical film, a heater in contact with an inner surface of the film, and a roller forming a nip portion via the film together with the heater. When an image forming apparatus provided with such an image heating device performs continuous printing using small-sized paper, a phenomenon occurs in which temperature of a region through which the paper does not pass in a longitudinal direction of the nip portion gently increases (temperature rise in a sheet non-passing portion). If the temperature of the sheet non-passing portion becomes too high, individual parts in the device may be damaged, or if printing is performed by using large-sized paper while the temperature rise in the sheet non-passing portion is generated, high-temperature offset of toner may occur to the film in a region corresponding to the sheet non-passing portion of the small-sized paper.
As one of methods for suppressing such a temperature rise in the sheet non-passing portion, a device which switches heat generation distribution of a heater according to a size of a recording material by dividing a heat generating resistor on the heater into a plurality of groups (heat generating blocks) in a longitudinal direction of the heater is proposed (Japanese Patent Laid-Open No. 2014-59508).
Meanwhile, a conductive member for supplying power is connected to the heater, and temperature distribution of the heater is considered to be non-uniform due to heat radiation from the conductive member and an electrode to which the conductive member is connected.